1. Field of the Invention
This invention relates to an image forming apparatus provided with an intermediate tray, such as a copying machine, a printer or a facsimile machine.
2. Description of the Related Art
Image forming apparatuses such as copying machines, printers and facsimile machines include apparatuses which can effect both-surface image formation, i.e., forming images on the front and back surfaces of a sheet material, and apparatuses of the multiplex type which effect image formation by superposing images on the front surface of a sheet material.
In an image forming apparatus shown in FIG. 3 of the accompanying drawings, originals (not shown) are successively set at a predetermined position on platen glass 3 by the use of an automatic original feeding device 2 provided on top of an image forming apparatus body 1. One of the originals set on the platen glass 3 is scanned by an optical system 4 and is exposed onto a photosensitive drum 5 rotating in a clockwise direction. An electrostatic latent image formed on the photosensitive drum 5 is developed into a toner image by toner supplied from a developing device 6.
Also, in this image forming apparatus, sheet materials S stacked on one of a plurality of sheet supply portions (a sheet supply cassette and a sheet supply deck) 7, 8, 9 are successively supplied to the photosensitive drum 5. The toner image on the photosensitive drum 5 is transferred onto the sheet materials S supplied to the photosensitive drum 5, by a transfer charger 10. The sheet materials S onto which the toner image has been transferred are sent to a fixating device 12 by a conveyor 11, and the fixation of the toner image is effected by the fixating device 12.
When the fixation of the toner image is terminated, the copying on one surface of the sheet materials S is terminated, but in the case of two-surface copying, copying on the other surfaces of the sheet materials S is effected subsequently and therefore, the sheet materials S are not discharged out of the apparatus, but are once stacked on an intermediate tray 13 in the image forming apparatus body 1. That is, in the case of two-surface copying, the sheet materials S on which the toner image has been fixated by the fixating device 12 are directed to a reversing path 15 by a reversing flapper 14 changed over to a position indicated by broken line, and are conveyed in the direction of arrow a, whereafter the sheets S are returned in the direction of arrow b and are directed to an intermediate tray discharge path 16, and are discharged onto the intermediate tray 13 by a pair of discharge rollers 17 or 18.
The sheet materials S onto the first surfaces of which the toner image has been transferred in this manner are successively stacked on the intermediate tray 13 with the first surfaces thereof facing upwardly.
When the copying onto the second surfaces is started, the sheet materials S stacked on the intermediate tray 13 are successively fed out from the lowermost one by a sheet feeding roller 19. As regards the sheet materials S thus fed out by the sheet feeding roller 19, the lowermost sheet is separated from the other sheet materials by a pair of separating rollers 20 and only the lowermost sheet is fed to the photosensitive drum 5. The toner image on the photosensitive drum 5 is transferred onto the second surface of the sheet material S fed to the photosensitive drum 5, by the transfer charger 10. The sheet material S onto the second surface of which the toner image has been transferred is sent to the fixating device 12 by the conveyor 11, and the toner image thereon is fixated by the fixating device 12.
When the fixation of this toner image is terminated, the copying on the both surfaces of the sheet material S is terminated, and the sheet materials S are successively discharged onto a sheet discharge tray 23 outside the apparatus by a pair of inner sheet discharge rollers 21 and a pair of outer sheet discharge rollers 22.
Reference is now made to FIGS. 4A to 4J of the accompanying drawings to describe the operation when a plurality of one-surface originals are to be copied on beth surfaces of a plurality of sheet materials S as a specific example of the two-surface copying operation in this image forming apparatus. Here, four one-surface originals are copied on both surfaces of each of two sheet materials S.
Four predetermined one-surface originals are first stacked and set on the original supporting table 2A of the automatic original feeding device 2 in the order of a first original P1, a second original P2, a third original P3 and a fourth original P4. In this state, a copying start key is depressed (FIG. 4A).
When a copying start signal is input, the automatic original feeding device 2 sets the lowermost fourth original P4 at a predetermined position on the platen glass 3. The optical system 4 scans this fourth original P4. On the other hand, a first sheet material S1 is supplied from one of the sheet supply portions 7, 8, 9 to the photosensitive drum 5, and the toner image on the photosensitive drum 5 (the image of the fourth original 4) is transferred onto a first surface of the first sheet material S1 (FIG. 4B).
Subsequently, the automatic original feeding device 2 skip-operates the third original P3 and makes it pass on the platen glass 3 (FIG. 4C). Subsequently, the automatic original feeding device 2 sets the second original P2 at a predetermined position on the platen glass 3, and the optical system 4 scans this second original P2. On the other hand, a second sheet material S2 is supplied to the photosensitive drum 5, and the toner image on the photosensitive drum 5 (the image of the second original P2) is transferred onto a first surface of the second sheet material S2 (FIG. 4D).
Subsequently, the automatic original feeding device 2 skip-operates the first original P1 and makes it pass on the platen glass 3. On the other hand, the first sheet material S1 and the second sheet material S2 onto the first surfaces of which the toner images have been transferred are successively stacked on the intermediate tray 13 (FIG. 4E). Subsequently, the automatic original feeding device 2 skip-operates the fourth original P4 and makes it pass on the platen glass 3 (FIG. 4F).
Subsequently, the automatic original feeding device 2 sets the third original P3 at a predetermined position on the platen glass 3, and the optical system 4 scans this third original P3. On the other hand, the first sheet material S1 is supplied from the intermediate tray 13 to the photosensitive drum 5, and the toner image on the photosensitive drum 5 (the image of the third original P3) is transferred onto a second surface of the first sheet material S1 (FIG. 4G). Subsequently, the automatic original feeding device 2 skip-operates the second original P2 and makes it pass on the platen glass 3 (FIG. 4H).
Subsequently, the automatic original feeding device 2 sets the first original P1 at a predetermined position on the platen glass 3. The optical system 4 scans this first original P1. On the other hand, the second sheet material S2 is supplied from the intermediate tray 13 onto the photosensitive drum 5, and the toner image on the photosensitive drum 5 (the image of the first original P1) is transferred onto a second surface of the second sheet material S2 (FIG. 4I). Subsequently, the first and second sheet materials S1 and S2 onto the second surfaces of which the toner images have been transferred are successively discharged onto the sheet discharge tray 23 outside the apparatus, and the predetermined two-surface copying operation is terminated (FIG. 4J ).
Now, when the above-described two-surface copying is effected, it is often the case that the sheet materials S1 and S2 temporarily stacked on the intermediate tray 13 are attracted to each other by electrostatic attraction caused by corona charge in the copying process onto the first surfaces thereof. Accordingly, when the sheet materials S1 and S2 in the intermediate tray 13 are re-fed, they are often fed in their mutually superposed relationship and are jammed. Or the sheet materials onto the first surfaces of which the toner images have been transferred are sometimes curled under the influence of the fixating process, whereby they are jammed.
In such cases, it is desirable that the sheet materials which have become unusable due to the jam be removed from the conveyance path and such that the remaining sheet materials be usable. However, the remaining sheet materials lack the pages before them and are therefore out of order in the correspondence of page order with the originals. There has heretofore been no image forming apparatus capable of handling this situation.
Accordingly, in the above-described image forming apparatus according to the prior art, if sheet materials re-fed from within the intermediate tray 13 are jammed when a plurality of one-surface originals are copied on both surfaces of a plurality of sheet materials, it has been impossible to set unjammed sheet materials in the intermediate tray 13 and use them, and such sheet materials could not be used.